1. Jan 4, 2009

### Dmitry67

In 1915? (Schwarzschild's solution for the interior of the black hole)
But what happens inside the horizon is not falsifiable...

2. Jan 4, 2009

### Staff: Mentor

I think that as long as people recognize such things for what they are, it does not constitute an abandonment of falsifiability.

Basically, in this case, you would say: "The solution implies XXX, but we are unable to verify or falsify this." As long as no stronger statements are made in favor of XXX, it's fine.

3. Jan 4, 2009

### jambaugh

This used to bother me too until I thought it out carefully and realized the following.

The inability to view the interior of a black-hole's event horizon is exactly the same as our inability to observer the future (without waiting for it to become now). In essence the interior is always in the future of events outside.

For all we know the gravitational constant will triple suddenly inside the future light-cone of the Earth at 12:01am EST January 1 2012. This is not falsifiable today but we can wait and see.

Likewise if you wish to disprove a hypothesis about the interior of a black-hole's event horizon you need only jump on in and check. The fact that you can't then tell me about it (since I'm not fool enough to follow you) is no different from the fact that you can't go back in time and tell Einstein what the stock market did today.

We use the same "faith" about no sudden changes in the laws of physics over time by which we project past evidence to future predictions, to also project beyond the event horizon of black holes.

4. Jan 4, 2009

### Dmitry67

Well, there is a difference.

If I predict that tomorrow day will be 2 hrs shorter for mysterious reasons is falsifiable. Just wait until tomorrow. In fact, you can not provide any contreexample immediately for some theories, so you need to make an experiment - you need some time to prepair it. Even to provide a contreexample you already know from the past experience takes some time, you need to open your mouth and say some words.

So NOTHING is falsifiable IMMEDIATELY, in a t=0 interval.

But for the black hole you will NEVER know.... This is a difference...

5. Jan 4, 2009

### DaveC426913

I think he means "the future" in the strict metaphysical sense that "the future" is always yet to be, even if there are events in it that will become "the present".

i.e. we cannot know "an event in the future" until it stops being "in the future" and becomes "in the present".

I'm just not sure if that's a valid concept.

6. Jan 4, 2009

### jambaugh

No there isn't. Again as you reiterated nothing is falsifiable immediately nor into the past. We are swimming in event horizons, the boundary between past and future is an event horizon. (or more properly the future light-cone of an event is an event horizon). It is the existence of these event horizons which prevents us verifying a hypothesis about the future without going there. Similarly you can go into the interior of a Black hole's event horizon and verify/falsify any prediction there. You just can't get back out.

A black-hole is simply a little ball of "always the future" for anyone outside it.

Now we can falsify Einstein's theory about local regions of space-time.

Having done so we can define hypotheses about local regions of space-time 100years in our future as likewise falsifiable via our ability to test them in the present. There is that implicit assumption that physical laws don't change over time (or better said we incorporate any change over time into our definition of "physical laws").

How is this different from a not-so-bright astronaut who is about to fall into a black hole assuming Einstein's field equations still hold in his future?

He will not see a sudden change in the physical laws at the event horizon any more than we see one as we cross the infinite pages of event horizons separating our past and future from moment to moment. Locally there is no distinction. They are of the same type. The only difference is that we outside see all those pages become a tube from our perspective. But the infalling astronaut doesn't see any substantial difference. At the instant he reaches the event horizon of the BH he sees it locally as a piece of his future light-cone.

Now granted near the singularity at the center all bets are off because we cannot locally replicate those conditions. But between there and the surface it's just space-time locally like any other piece of space-time.

7. Jan 4, 2009

### Dmitry67

Ok, agreed, this is a good point. Still there is a problem

I agree that some suicidal experimenter can verify the laws of physics inside the black hole (any volunteers?). But the humankind will NEVER benefit from his research.

if we DO accept the falsifiability as an important rule, we should STOP all blah-blah-blah about the interior of the BH until... well, except for the kamikadze researches.

Just compare the status of the Higgs boson right NOW with the status of the Schwarzschild (Kerr) solutions of the interior of the BH.

Higgs: theoretical, we are almost sure, but it is not confirmed. So it is still a hypotesis because experiment has not been yet performed
Interior of the BH: Yeah, old well known, booooring stuff, check the book written in the beginning of the 20 century.

Now, we are going to know about the Higgs in about 1 year (I hope). Regarding the interiour of the BH, we will NEVER KNOW. So I ask you, how the status of these 2 HYPOTESIS can be so different? Nobody even calls the Schwarzschild (Kerr) equation a HYPOTESIS. It is called a SOLUTION. Feel the difference? :)

8. Jan 4, 2009

### Hurkyl

Staff Emeritus
Another thing to recognize is that science necessarily deals in extrapolation; if it didn't make any predictions about situations that have not been tested, then it wouldn't be very useful!

(Some extrapolations are so tame that many people have difficulty accepting that it's involved -- for example, the prediction that the sun will rise tomorrow -- but it's still an extrapolation!)

So the question boils down to what sorts of extrapolations are 'safe'. My understanding (I am not a scholar of GR) is as follows:

Space-time near the event horizon (both from the inside and from the outside) is predicted to be rather ordinary-looking, especially for a large black hole. It's only by looking at all of the space-time around it that you would notice anything unusual. And thus, there is little grounds for skepticism. In other words, the description of the interior of a black hole (at least, away from its singularity) appears to be that of known physics applied in its domain of validity.

9. Jan 4, 2009

### Hurkyl

Staff Emeritus
Of course. An object that satisfies an equation (or system of equations or other type of condition) is usually called a solution. And the Schwarzschild metric does indeed satisfy Einstein's field equations. (at least in the $0 \neq r \neq 2GM/c^2$ region)

10. Jan 4, 2009

### jambaugh

Right. Specifically the hypothesis is the field equations, or more precisely what they predict about trajectories of test particles, the solution is the prediction of the hypothesis.

Note on your qualifier, in appropriate coordinates the Schwarzschild solution is valid at the event horizon as well. You just get a coordinate singularity in the original form. We don't say for example that a solution to a well formed differential equation fails at r=0 just because we are using polar coordinates and thus there's a coordinate singularity there.

11. Jan 4, 2009

### jambaugh

Again I can coach another "future hypotheses can't benefit humanity in the past" e.g. we will not today benefit from assuming Maxwell's equations will hold 100years from now.

But be that as it may. You say "never" but you can't rule out the possibility that at some time in the distant future a very large black hole won't swoop down and engulf the entirety of humanity in which case a.) we will be able to verify/falsify Einstein's theory in the interior and b.) it might be damn useful to know how long we got until the tides rip us apart.

For that matter there have been made serious conjectures as to whether the entirety of the visible universe might not be interior to a very large black hole.

It is an important rule but not to be used mindlessly. Its purpose in the tool bag of the theoretician is to excise non-operational hypothesizes (such as the existence of a luminiferous ether.) It is perfectly operational to discuss what our hypothetical astronaut would see as he passes into a BH. For this test of operationality it is sufficient that one hypothetical astronaut could in principle test it. Once we agree that this is the case then we needn't actually sacrifice such an astronaut nor require he have the ability to tell us what he's observed. We have shown the hypothesis is operationally meaningful.

Now actual experimental confirmation is another matter... but that is not what we are talking about.

We can test and falsify the implications of Einstein's field equations in any region of space-time. Once that has been done then extrapolating them to other regions of space-time, be they the interior of a black hole or the future, is perfectly valid and reasonable.

I think you would see this clearly if you understood better the nature of "an event horizon" and the equivalence in nature (if not shape) between the one around a black-hole and the one keeping me from telling my past self tomorrow's stock market summary.

I will also point out that you are guilty of your own "sin" in that you are making hypotheses about the interior of a black hole, namely that it is causally incommunicado, said hypothesis being by your arguments non-falsifiable.
( If anyone should "stop all the Bla Bla Bla"...)

12. Jan 5, 2009

### Dmitry67

I agree with you. I even think that the importance of that tool is overestimated.

Max Tegmark used this example to illustrate that 'parralel universes' must have at least the same status as the interiors of BH.

In both cases we have gravity/QM operating smoothly Outside of the BH/In out branch of reality.

In both cases nothing magical happens on the Horizon/during the Quantum decoherence. Both processes are described mathematically.

So I can just replace few words in what you had said:

13. Jan 5, 2009

### jambaugh

Not so fast. First explain what you mean by "parallel universes" and explain how to go about getting your astronaut to traverse them. We know how to enter a black hole, you just fall in. If you're thinking of a Kerr black hole e.g. worm-hole then there are some issues about crossing the second horizon... but let that be.

But I am not arguing that we de-emphasize the importance of falsifiability. To the contrary, I would insist scientific hypotheses be operationally meaningful. Components which are not should be identified as elements of a model!

If you are thinking of something silly like Everett's many worlds then ... well I can say a lot (and have) about that. Everett's many worlds are by definition not operationally meaningful and thus should be called a Everett's many-worlds model instead of an interpretation.

Carefully re-read what I have said. I did not say that falsifiability should be de-emphasized but that it should be applied consistently and with its purpose (testing operationality) in mind.

14. Jan 5, 2009

### Dmitry67

1 Well, in Everetts interpretation Many Worlds is an axiom.
I believe in a modern interpretation, Many Worlds based on the Quantum Decoherence
So the Many words are the consequence, not an axiom:

Max Tegmark
http://arxiv.org/abs/0704.0646v2

So in order to go into a parralel universe we need to do something different based on the random QM event. For example, if I see a dead Shroedinger cat, then another me is watching the alive one.

2 It is an offtopic, but could you explain or point to the right place... what are the problems with the second horizon?

15. Jan 6, 2009

### jambaugh

In which case his worlds are mathematical constructs and not physical per se...
Again this "interpretation" is not operational and so should be called "model". I understand quantum decoherence...= irreversible entanglement with the episystem. I wouldn't call "many worlds" a consequence. There is still an implicit assumption=axiom. Decoherence does not contradict the Copenhagen interpretation so it can't be said to imply any other interpretation.

Different from what? You are getting "entangled" in counterfactuals. The "you" that does "something" is distinct from the hypothetical " you' " who does "something different". The second can't communicate with the first any more than Tom Sawyer can communicate with me. Tom Sawyer is a fictional character, ....

And I assert that "No, a demon can see the future and picks the outcome to be consistent with QM's predictions and what he knows about future experiments on the quantum system ... just because he wants to be nasty...oh yes and he has big red horns and a curly black mustache". How is my hypothesis less non-falsifiable than yours?

The Everette many worlds model reminds me of the old song "I knew an old lady who swallowed a fly..." it tries to cure a minor unaesthetic issue by introducing a very inelegant "horse-sized" assertion.

I have a vague recollection of there being a boundary of infinite temperature inside the Kerr black hole which must be crossed if you're going to avoid the singularity. This is to say no information could actually make it through even though there are classically causal paths through. I just did a google search and I think this is what is now referred to as the "blue sheet".

16. Jan 6, 2009

### Dmitry67

Well,

http://en.wikipedia.org/wiki/Quantum_decoherence
So, after QD we have 1/2 alive cat + 1/2 dead cat. These cats dont interefere.

You have a choice: to assume that both cats do exists (Multiworlds), or to invent some new mechanism (like wavefunction collapse) to explain why the whole universe had randomly but consistently chosen one particular branch.

In that case you whould deal with the Ocamms razor (why do you need it if everything is already explained without it?) Your mechanism will be non local and you will have to answer questions like 'as QD is not immediate, at what moment the second branch dissapear? Why any particular branch is chosen? You say, randomly? What is a probability? Bayesians or Frequentisits? Why? et cetera, et cetera, et cetera...

And why? Why do you need all that weird stuff? Just because the very idea of parralel universes is so weird? because it is so easy to assume that space,or time are infinite, but for some reason we can not aqssume that WE exist in the infinite number of copies?

17. Jan 6, 2009

### jambaugh

No after QD you have either a live cat or a dead cat with classical 50-50 probability.

The "many worlds" are many worlds of possibility. Its no different from standard classical probability. If I flip a coin I can imagine it landing heads and imagine it landing tails... two worlds in my imagination. Afterward those two worlds still exist in my imagination but I qualify one as "what might have been". I don't need a fancy mechanism or to worry about "classical probability collapse" or anything. Both "worlds" continue to "exist" in my brain.
The actual coin behaves as it behaves and I observe it as I observe it.

In order to see actual quantum behavior for cats you must first freeze the cats to near absolute zero then you'll need a very large number of frozen cats so you can do interference experiments and get a whole interference pattern. Of course the cats can't survive such an experiment so "alive vs dead" is not going to be a quantum observable anyway. Remember a cat is a heat engine and thus any quantum interaction with them by definition must decohere almost immediately.

Let me put it (decoherence) another way. Think of entropy as entanglement with the environment. (Recall that partial traces of the zero entropy joint density operator yields a non-zero entropy density operator for a partial system.) Now once a quantum system interacts with its environment it can no longer be sharply described (i.e. with a wave-function) alone. It must either be described with a density operator or to preserve the sharp description you would have to describe the system plus that part of the episystem it has interacted with and then only if that part of the episystem has been observed sharply before hand. (That is unless you have been very careful with the type of interaction i.e. you've made a measurement or are preparing the system in a sharp mode). T

You in other-words would need to observe a cross section of the system's past light-cone up to the point you still want to describe the system sharply and likewise the future light cone of that whole system. And given that bigger system has also interacted with its environment....

If you do not do this then you introduce classical random variables into the system upon which the outcome of the future experiment on that system will depend. Thence the "collapse" of the system's wave-function is no different from the "collapse" in the expectation value for a lotto ticket once the drawing occurs, a classical probability collapse.

There is no problem to be solved by invoking Everett's many worlds. Wave function "collapse" is only a conceptual problem if you confuse the wave-function with the actual system. A lotto ticket is not the cash prize (or a superposition of many cash prizes). A wave-function is not an electron. Remember that quantum interference is more fundamental than classical wave interference. Classical waves are composites of quantum systems. Why go backwards and try to describe a quantum system as a classical wave (function)? Instead understand that the wave-function is a representation of what we know about how the system behaves.

With respect to the measurement "problem" and wave-function "collapse" consider this. The distinction between "before" and "after" is by definition separated by an environmental interaction. The variables describing the system "after" differ from those "before" said difference depending on the "in between" interaction which is necessarily probabilistic. It is not the system that suddenly changes. It is our description of the system. We choose a new wave-function because via the measurement process the system is different. The system change can be gradual or even delayed. When we interact with the measuring device our knowledge about the system changes in a classical way and we then use an updated wave-function to describe it.

Note also the intimate involvement of thermodynamics in the measurement process...(you amplify a signal and must dissipate heat into an entropy dump). Google the terms "thermodynamic" and "quantum measurement" to see what I mean. The system has changed by assumption and so its description changes by assumption and due to its interaction with a measurement device you can only describe it continuously by describing both it and the large scale variables of the measuring device which register its outcome, said variables now being highly correlated with the quantum variable of the system being measured.

The "many worlds" of Everett are "many worlds of possibility" not of reality...and what is more there are just as many of these prior to the measurement event as there are after it...they consist of the many possible configurations of the measuring device's heat dump prior to the act of measurement. You fundamentally can't describe the measuring device with a wave function due to its necessarily thermodynamic nature. It must be described at best by a density operator, classical probabilities and all. As such sequences of measurements are necessarily non-deterministic unless your are careful about which measurements you make. No mystery, no need to puzzle over EPR experiments except to carefully avoid counterfactual hypotheses.

18. Jan 6, 2009

### jambaugh

Let me add something about the concept of superposition. Starting with a classical example, If I am traveling north-west I am in a superposition of traveling north and traveling west. This doesn't mean I am traveling in two directions, only that the description of the direction I am traveling does not fall along standard cardinal directions.

Likewise when a quantum system is "in superposition" it is only relative to some choice of observable in which case the system's mode is not an eigen-mode of that observable. But the system is in only one mode, not two at once. It is just that we are using some observable other than the one about which we have full knowledge.

It might be even better to understand it in terms of one observable being a superposition of another.

In the case say of an electron passing through a double slit. Our "cardinal" observable is position because we grew up thinking of electrons as classical point particles, and because that is the observable we use in our electron detectors. But the electron is in a single mode described by another observable rather less intuitive than position.

The "collapse" of the electron to a position eigen-mode is no weirder than if in my classical example I suddenly turned north and my superposition of directions suddenly "collapsed" into a single direction. A wave-function "collapse" is a turn not a catastrophe!

Last edited: Jan 6, 2009
19. Jan 7, 2009

### Dmitry67

I am trying to make my posts short as it is not mathematics and words 'space', 'time', 'probability' mean different things for different people. So,

If you see it that way then for you the world in not symmetric, because one branch (say, dead cat) is a 'real' one while another one was just a 'lost opportunity'. For me it is symmetric.

So your view looks like exactly like a Multi-World observed using a so called frog's view (a view of an observer, as Max Tegmark defines it). We are almost on the same page, you just deny or ignore the 'bird's view' so you analyze only one branch of reality.

If I had correctly explained it could you give a hint why you prefer an assymetric view?

20. Jan 7, 2009

### jambaugh

Actually no. My view is that both "worlds" are conceptual, symmetry restored. But we pick the conceptual world which fits our experience. Experience is singular and so there's nothing with which to define a symmetry.

(Actually there is, and that is the covariance group describing the relationship between different observers' experiences. But that again is all within a single actuality.)

At the quantum level I deny "reality" all together. It is exactly the assumption of an objective reality with objective state which leads to all the problems conceptualizing QM.
You can still describe objects in the more general language of processes. You replace "reality=what is" with "actuality=what happens". When "what happens" fits an objective ontological model then we say we are considering phenomena at the classical level, as for example when we are talking about "the moon". But when we push the limits of observation this correspondence breaks down and we must stick to describing processes only.

The vertical polarization 'ket' of a photon is not a description of the photon but rather a description of the class of photon source devices. Dually the vertical polarization 'bra' corresponds to a class of photon "sinks" i.e. detectors. They are modes of production/registration for a physical process not states of a physical object.

The math tells us how to express say an oblique polarization mode in terms of a superposition of vertical and horizontal modes and it also tells us the probability of one mode detector registering what another mode source produces.

Phenomena not objects ... observations and measurements not states. This is what is operationally meaningful in the framework of the empirical epistemology of science.